1. Field of the Invention
The present invention relates generally to television signal processing systems and, more particularly, is directed to a television signal processing system for improving the vertical resolution of a reproduced picture.
2. Description of the Prior Art In accordance with the existing NTSC system, as shown in FIG. 1A, at the pick-up side only odd-numbered scanning lines such as l.sub.11, l.sub.13, . . . are scanned during the odd field period, while only even-numbered scanning lines such as l.sub.22, l.sub.24, . . . are scanned during the even field period whereby the 2:1 interlaced scanning for one frame of 525 scanning lines is carried out by a pair of odd and even field periods to thereby sequentially transmit television signals S.sub.11, S.sub.13, . . . ; S.sub.22, S.sub.24, . . . corresponding to picture information on the respective scanning lines and then such television signals are displayed on a picture tube or the like. According to such a scanning technique, the transmission band can be reduced by about 1/2.
In the case of this interlaced hereinabove, however, there is a time difference of 1/30 of a second that the picture information on a desired scanning line, for example, l.sub.13 is displayed on the picture screen of the picture tube until the picture information on the scanning line l.sub.33 is displayed at the same position of the picture screen. As a result, there is optical interference with the picture information displayed on the intermediate position therebetween or the adjacent scanning lines l.sub.22 and l.sub.24 thus causing a so-called inter-line flicker which causes the vertical resolution of the reproduced picture to be lowered.
This inter-line flicker becomes more conspicuous on the picture screens of present day television receivers which have brighter picture tubes.
In order to avoid lowering the vertical resolution of the reproduced picture due to the inter-line flicker, as shown in FIG. 1B, the interlaced scanning is carried out such that picture information of, for example, only the odd-numbered scanning lines l.sub.11, l.sub.13, . . . are transmitted at every field. However, according to this interlaced scanning, the picture information of, for example, the even-numbered scanning lines l.sub.22, l.sub.24, . . . are not transmitted so that the vertical resolution of the reproduced picture is essentially low.
It is also known that if the scanning frequency of the interlaced scanning system is selected to be 31.5 kHz, which is twice the scanning frequency of 15.75 kHz of the existing system, and picture information consisting of 525 scanning lines is displayed at every 1/60 second, the inter-line flicker can be removed and the vertical resolution of the reproduced picture can be improved. In this case, however, a transmission band width twice as wide as that of the existing system becomes necessary and this system is not compatible with the existing television transmitting system.
Therefore, in order to improve the vertical resolution of the reproduced picture lowered by the above-mentioned inter-line flicker, studies have been undertaken of an IDTV (improved definition TV) in which the existing broadcasting system is not altered and the interlaced scanning is carried out at the television receiver side and an EDTV (extended definition TV) in which compatibility with the existing broadcasting system is maintained and the broadcasting system is improved and altered.
The fundamental technology common to such IDTV and EDTV is based upon the sequential-scanning/double-scanning display method in which signals corresponding to the scanning lines whose signals are not transmitted are interpolated at the receiving side. Accordingly, in the case of a still picture, the complete interpolation of a signal is possible.
However, in case of a real, moving picture (i.e. alive picture), the picture quality of mainly the outline portion of the reproduced picture is deteriorated and the smooth motion of the real moving picture is lost. In order to diminish the deterioration of the picture quality of the real moving picture, it may be considered that upon carrying out the sequential scanning, the interpolation between the fields is carried out for the still picture portion whereas the interpolation within the field is carried out for the real moving picture portion. In this case, it becomes necessary to provide a judging circuit for judging whether the picture portion to be reproduced is the still picture portion or the real moving picture portion.
Since the interlaced scanning can be regarded as a two-dimensional sampling in the time-to-vertical frequency area, if a picture to be reproduced is a still picture, the scanning frequency f.sub.IS and the higher harmonic wave thereof are expressed as shown in FIG. 2A. For this reason, a conventional real moving picture judging circuit is one which fundamentally uses a vertical comb filter having the characteristic shown in FIG. 2B to judge the picture to be reproduced as a still picture when the frame difference output is zero. However, according to the judging circuit based on the frame difference output, it is not possible to detect a real moving picture with a frequency of 30 Hz. Even when a field difference output is used to detect a real moving picture, in the case of the interlaced scanning system, no sampling point originally exists at the position shown by a cross mark x in FIG. 2A so that the real moving picture can not be judged by the field difference output.
Further, as one system of the above EDTV, there is known a system called "Ivision" which is seen in the technical report of The Journal of the Institute of Television Engineers of Japan, No. 21, Vol. 9 (Oct. 1985).
According to this "Ivision" system, as shown in FIG. 3A, an image is picked up by sequential scanning of 525 lines during one frame period of 1/30 second and then, as shown in FIG. 3B, the television signal is divided into television signals S.sub.11, S.sub.13, . . . corresponding to the odd-numbered scanning lines l.sub.11, l.sub.13, . . . and television signals S.sub.12, S.sub.14, . . . corresponding to the even-numbered scanning lines l.sub.12, l.sub.14 . . . , or converted into an interlaced scanning signal substantially equal to a signal according to the NTSC system, and then broadcast. In the existing television receiver, this interlaced scanning signal is displayed as it is, whereas in the television receiver of the "Ivision" system, as shown in FIG. 3C, television signals which are not transmitted (for example, television signals S.sub.12, S.sub.14, . . . in the first field and television signals S.sub.11, S.sub.13, . . . in the second field, etc.) are interpolated within the frame and then sequential scanning is presented, thus the television signal of the same frame being displayed twice each during the period of 1/30 second.
According to this system, on the basis of the simple interpolation of the scanning lines, the vertical resolution of the reproduced picture can be improved by a relatively simple circuit arrangement.
However, in the case of the "Ivision" system, the picture is picked up by the interlaced scanning at every 1/30 second so that both the television receiver of the existing television system and the television receiver of the "Ivision" system can not avoid a problem of deteriorated picture quality such as when a real moving picture can not be moved smoothly and so on.